Spin- and deformation-dependent orbital M1 strength in rare-earth nuclei

Abstract

The M1 excitations in three isotope chains, 142,146,148,150Nd, 144,148,150,152,154Sm, and 156,158Gd, are studied within the quasi-particle random-phase approximation using a mean field given by a deformed Woods-Saxon potential and including quadrupole-quadrupole and spin-spin residual interactions. A residual rotation-vibration coupling ensures the exclusion of the spurious state. The behaviour of the M1 strength distribution is studied systematically in the whole range of experimentally explored excitation energies and compared with the large variety of experimental information, which includes both low-lying orbital and higher-lying spin-flip 1+ excitations. We have found a quadratic dependence of the M1 strength summed up to 4 MeV on the nuclear deformation reproducing at the same time the main features of the low-lying M1 spectra. The double-peaked structure of the spin M1 strength distribution found experimentally in several nuclei is qualitatively reproduced and interpreted as isoscalar and isovector peaks.

Magnetic dipole excitations in nuclei: Elementary modes of nucleonic motion

“…It is the residual particle-hole interaction acting in the spin-isospin channel that shifts this spin M 1 strength to higher energies as can be seen e.g. in schematic model (De Coster and Heyde, 1991a;De Coster et al, 1992;Zawischa and Speth, 1994) and in RPA studies (Sarriguren et al, 1996(Sarriguren et al, , 1993(Sarriguren et al, , 1994.…”

“…For larger strengths of the spin-spin proton-neutron interaction as used by Sarriguren et al (1996Sarriguren et al ( , 1993Sarriguren et al ( , 1994, the spin strength becomes concentrated more into a full isoscalar and isovector part with proton and neutron configurations strongly mixed. obtain results somewhat intermediate between the two more extreme cases of very weak coupling and strong coupling between the individual proton and neutron spinflip M 1 configurations.…”

SpinM1 excitations in deformed nuclei from self-consistent Hartree-Fock plus random-phase approximation

“…1 the results obtained from a deformed Woods-Saxon potential with the parametrization of Tanaka et al ͓44͔ used in Refs. ͓13,14,20͔. In this figure, as well as in the remaining figures to be discussed later, the strength B (M 1) is summed over energy bins of 80 keV to facilitate the comparison to experiment.…”

Nuclear shape transitions and elastic magnetic electron scattering

“…Electron scattering can be also used as an additional tool to complement the information obtained from other probes. This could be the case of magnetic dipole (M 1) excitations in nuclei, where it is well known that complementary information is obtained when using different electromagnetic (γ, γ ′ ), (e, e ′ ) or hadronic (p, p ′ ) probes [8,9]. Electron scattering may also be used as a tool to investigate weak processes, such as parity-violating electron scattering [10][11][12] or other processes involving neutrinos [13,14].…”